Multiple switchboard for telephone-exchanges.



PATEINTED OCT. 25', 1904.

. Y M. G. KELLOGG.

MULTIPLE SWITGHBOARD FOR TELEPHONE EXCHANGES.

APPLICATION FILED FEB. 28, 1891.

m MODEL;

' UN TED STATES Patented October 25, 1904.

PATENT OFFICE.

MILO G. KELLOGG, OF CHICAGO, ILLINOIS, ASSIGNOR TO KELLOGG SWITCHBOARD AND SUPPLY COMPANY, OF CHICAGO, ILLINOIS,

A CORPORATION OF ILLINOIS MULTIPLE SWITCHBOARD FOR TELEPHONE-EXCHANGES.

SPECIFICATION forming part of Letters Patent No. 773,506, dated. October 25, 1904.

Application filed February 28, 1891- Serial No. 383,260. (No model.)

To (tZZ whom it may concern:

Be it known that I, MILO Gr. KELLOGG, of Chicago, in the county of Cook and State of Illinois, have invented certain new and useful Improvements in Multiple Switchboards for Telephone-I lxchang es, of which the following is a full, clear, concise. and exact description, reference being had tothe accompanying draw: ings, forming a part of this specification.

My invention relates to a telephone exchange system in which the lines are grounded at their outer ends and are grounded at the central oflice.

Briefly stated, my invention consists in connecting the telephone-lines in pairs with the I different switches on the boards, there being on each board one switch for each pair of lines and each switch having two contactpieces suitably placed and insulated, one of the lines of a. pair of lines being connected with one of said switch contact-pieces and the other line with the other switch contact-piece, and in switch-pl u gs, apparatus, and connections by which with such lines and switch connections the calls of the subscribers may be received and promptly attended to and the usual operations of the exchange gone through with.

Figure 1 is a front view of a section of the switchboards. Fig. 2 shows sections of two boards A and A with four lines connecting to them, four annunciators for the lines, with their connection to their respective lines and to the ground, and a pair of switch-plugs lo cated at each of the boards and connected to the operators apparatus and to their own special apparatus, which will hereinafter be described. Fig. 3 shows in diagram a sub scribers-station apparatus. The switches of the lines are marked a a and Zr 6, the two former being located on the two'boards shown and the two latter being also located on the two boards shown, respectively.

Z Z are the switch-holes through the fronts of rubber strips of the shape substantially as shown and on which the metal parts of the switches are mounted. These holes are preferably square or rectilinear. To one side of the center-of the holes are the contactsprings g g. On the, opposite sides of the center of the holes and along'the surface of 5 the holes are placed the contact-pieces j There is one spring 9 and one contact-piece j for each switch. V

' Four lines are shown in the drawings. Line ais connected with contact-springs g g of 55.

switches a a and line a with contact-pieces j; of the same switches. In like manner lines I) and b are connected with springs g g and pieces 1' respectively, of switches b b.

N are annunciators, and w w are retardation-coils, one annunciator and one reta'rda tion-coil for each line. The line is connected to theground through its annunciator and 1 retardation-coil, and the annunciator is located at the board where the calls of the line are to 5 I be answered.

D D are a pair of switch-plugs adapted to be inserted into any switch at their board and I to form connections when inserted, as will hereinafter be described.

7t n are the rubber insulations of the plugs, and mm are the two contact-pieces'of a plug. When a plugis inserted into aswitch, it may be inserted in such a direction that its piece 72?. forms connection with spring g and its 75 piece m forms connection with contact-piece j of the switch or in the reverse direction, so thatm forms connection with j and m forms connection with g.

For each plug there is a switching device, into which any other plug located at its board may be placed and Which has a contact-piece which connects with the contact-piece m of the plug thus inserted. The contact-piece of this switching device is connected through a flexi- 8 5 for switching forms connection with plate 0 andwith the ground through such connection. The contact-piece m of plug 1) is similarly constructed and normally connected with the ground.

Y is a looping-in switch with contacts 9) p q q and connections by which the operators telephone may be looped into said cordcircuit.

There is one test-battery B, one clearingout annunciator 0), two calling-keys K K, and one looping-in switch Y for each pair of cords.

B is the operators calling-generator, and t is her telephone. v

1 is an induction-coil, the secondary coil of which is in circuit with the operators telephone.

T is a test-plug which terminates a flexible cord-circuit and the contact-piece '2' of which is adapted to be brought for testing into connection with either of the pieces g or 7' of any switch at its board or with spring 9 of any plug switchingdevice atits board. The other end of said flexible cord-circuit is connected to ground through the primary of the induction-coil.

The two keys K K of a pair of plugs are connected into their cord-circuit, and their two levers are connected with the two contacts m m, respectively, of the plugs. The lower contacts of the key are connected with one side of the calling-generator and the other side of the generator is grounded. Each operator has as many pairs of plugs as she may reasonably require for her work, and they are connected to their special apparatus and to the operators apparatus substantially as shown and as heretofore described.

In the subscribers-station apparatus, (shown in Fig. 8,) l is the telephone-switch, 2 is the signal-receiving bell, 3 is the calling-generator, 4 is the subscribers telephone, and 5 is a calling-key. The generator is constructed with the usual automatic device whereby it is shunted or switched from the line-circuit while not operated. The insulated contactpiece on the shaft of the armature, to which is connected one end of the armature-wire and which conducts the generated current to line through the contact-springs provided for it, is a half-circle, the remaining part of the circle being an insulation, as shown. The key 5 is provided with two pairs of contacts, as shown, one pair being normally closed and the other pair normally open, and when the key-lever is depressed the normally closed pair of contacts is opened and the normally open pair is closed. The connections of the key to the contact-springs of the generator and to the line-circuit is as follows and as shown: The spring-lever which forms one of the contacts of each pair of contacts is connected with one side of the main-line circuit. The two other contacts of the pairs of contacts are connected to the two contact-springs,

respectively, of the generator. As before stated, one end of the armature-coil is con nected with the half-circle contact-piece, and against this piece the springs alternately press while the armature is being turned. The other end of the armature-coil is connected with the other side of the main-line circuit.

It is well known that when calling-genera tors are operated a current of one polarity is generatedduring one half of the revolution of the armature and a current of the other polarity is generated during the other half of the revolution of the armature. The two contact-springs are so placed with reference to the armature that one of them takes a cur-' rent of one polarity and the other takes a current of the other polarity.

It is apparent from the above description of the apparatus and connections that when the generator is being operated and the key is not depressed a current of one polarity will go to the line-circuit, but when the key is depressed a current of the other polarity will go to line.

The line-annunciators should preferably be polarized annunciators and should preferably be connected in their respective line-ci rcuits in such a direction that they are operated when the subscribers generator is turned and his key not depressed. The clearing-out annunciators of the exchange may be ordinary nonpolarized annunciators.

The operation of the system is as follows: hen a subscriber desires to send in a call, he will operate his generator withoutdcpressing on his key and his annunciator will indicate a call. The operator at the board where the call is indicated then places plug D of a pair of her plugs into the switch of the line and in such a direction in the switch that the contact-piece m of the plug forms connection with that contact-piece of the switch which is connected to the line. She then moves the lover of the looping-in switch of the pair of plugs into such a position that her telephone is in circuit with them and finds out by conversation what line is wanted. She then tests theline wanted, andif it is free or unswitched she connects the contact 112/ of the other plug, D, with the line wanted. Then by pressing on one or the other of the callingkeys she may send a calling-current through either line. When the line wanted does not have its switch with a plug inserted, she tests the line by placing the contact-piece 11 of her test-plug in connection with that contact of the switch which is connected with the line, and if the line tests free or not in use she places the other plug of the pair of plugs she is using for the connection into the switch in such a direction that the piece m of the plug forms connection with that contact of the switch which is connected with the line.

As heretofore described, when the plug is inserted into a switch in such a direction that its piece m forms connection with one of the contact-pieces of theswitch the piece m of the plug is then in connection with the other whose switch is already a switch-plug, she

merely inserts her test or switch plug, as the case may be, into the switching deviceof the plug inserted intothe switch, and she thereby makes connection with such line.

When the operator on receiving the call of aline finds that a switch-plug is already in the switch of the line, she connects with the line through the switching device of the plug. When a subscriber desires to send a clearingout signal, he presses on his key 5 and operates line.

his generator, and a current will go to the Oil'- cuit, which will operate the clearing-out annunciator in the circuit. This current is, however, of the opposite polarity of the current which operates her line annunciator; otherwise that annunciator might indicate and give a false signal that the subscriber desired a connection. comprehends, therefore, clearing-out annunciators that respond to clearing-out signals and line-annunciators that only respond tocalling-currents transmitted by subscribers. Thus the line-annunciators may be polarized and the calling-currents be of a character to operate them, while the clearing-out annunciators may bev oppositelypolarized or neutral, so that they respond to clearing-out currents that do not affect the calling-annunciators. The difl'erent polarized annunciators should be connected in the same direction in their respective circuits.

The operation of the test system is as follows: 'VVhen a line is not switched, it is not in circuitwith a battery. When it is switched, it has in circuit with it the battery of the pair of cords used in testing. 'When the test is applied and the line is switched, there is a circuit from the ground through the primary of the induction-coil to the contact of the line where the test is made, thence to the contact of the line where the line is switched, thence through the test-battery to the other line, and thence to both ground connections of the other As the operators telephone and the secondary of the induction-coil are then on closed circuit, the telephone will indicate the closing of the battery-circuit, and the operator will thereby know that the line is in use. When the test is made and the line is not "switched, no circuit is established which contains a battery, and as her telephone will therefore not indicate she will know that the line is free to be connected to.

coils.

The clearing-out system by Letters Patent It will be seenthat when two lines are con nccted together for conversation the circuit isjconnecteol to ground at the central ofiice through the annunciator. and retardation-coil of each line. resistance and high retardation, so that such ground connectionwill not seriously affect the talking-circuits. The annunciators themselves have so much retardation that in certain places it maybe considered unnecessary to use special retardation-coils.

WVhen a signal-current is sent from the cen- These instruments areof large tral oflice to either line, it goes to ground through the circuit of the line and the subscribers-station bell and also to groundat the central oflice through the lin-annunciator and retardation-coil. such resistance that when the signal is thus made there will not enough current pass through them to operate the annunciator. In the system which I have shown line-annunciators are placed with the retardationcoils in the ground connections of the lines. Certain features of my invention are applicable to exchanges'in which annunciators are not used and connected, as shown and described, in the circuit with the retardation For instance, the annunciators need not be used and the calls may be sent to the central office by means of special calling cir- These last should be of r cuits and systems, as in the well-known Law and American district systems. The advantage in such a system of operation in having the lines grounded at the central office is that there is less inductive disturbance in telephone-exchanges in which the lines are nor.

jurious efiect on the general operation of the I exchange.

With this system and organization for multiple switchboards only one-half as many switches are requiredfor a given number of lines and twice as many lines can be placed in a given space as in the usual multiple switchboard system. it therefore doubles the capacity of a gimn-sized'multiple switch: board. p

The system of switching here-in shown and described is like that of my application Serial No. 383,002, from which this case is distinguished by the use of annunciators or retarda; tion-coils in the groundconnections of the line at the central oiiice.

Iclaim as my invention and desire to secure 1. In a telephone-exchange system-,telephone-lines divided into pairs, annunciators for said lines, one annunciator for each line, and switches for said lines on a switchboard,

one switch for each pair of lines, each switch having two contact-pieces to which the two lines of its pair are respectivelyconnected,'

' &

and each line being grounded through its annunciator, in combination with pairs of switchplugs, the plugs having each a contact-piece, the two contact-pieces of a pair being connected by a flexible conducting-circuit, and a test-battery in each of such conducting-circuits, each plug being adapted to be inserted into each switch in two positions or directions, in one of which said contact-piece of the plug is in connection with one of the contact-pieces of the switch and in the other of which said contact-piece of the plug is in connection with the other contact-piece of the switch, substantially as set forth.

.2. In a telephone-exchange system, telephone-lines divided into pairs, retardationcoils for said lines one retardation-coil for each line and switches for said lines on a switchboard, one switch for each pair of lines each switch having two contact-pieces to which the two lines of its pair are respectively connected, and each line being grounded through its retardation-coil, in combination with pairs of switch-plugs, the plugs having each a contactpiece the two contact-pieces of a pair being connected by a flexible conducting-circuit, and

a test-battery in each of such conducting-circuits, each plug being adapted to be inserted into each switch in two positions or directions, in one of which said contact-piece of the plug is in connection with one of the contactpieces of the switch and in the other of which said contact-piece of the plug is in connection with the other contact-piece of the switch,substantially as set forth.

3. In a telephone-exchange system, telephone-lines divided into pairs, annunciators and retardation-coils for said lines, one annunciator and one retardation-coil for each line, and switches for said lines on a switchboard, each switch having two contact-pieces to which the two lines of its pair are respectively connected each line being grounded through its annunciator and retardation-coil, in combination with pairs of switch-plugs, the plugs having each a contact-piece, the two contactpieces of a pair being connected by a flexible conductingcircuit, and a test-battery in each of such conducting-circuits, each plug being adapted to be inserted in each switch in two positions or directions, in one of which said contact-piece of the plug is in connection with one of the contact-pieces of the switch and in the other of which said contact-piece of the plug is connected with the other contact-piece of the switch, substantially as set forth.

4. In a telephoneexchange system, telephone-lines grounded at their outer ends and divided into pairs, annunciators for said lines, one annunciator for each line and switches for said lines on a switchboard, each switch having two contact-pieces to which the two lines of its pair are respectively connected, and each line grounded through its annunciator, in combination with pairs of switch-plugs, the plugs having each a contact-piece, the two contactpieccs of a pair being connected by a flexible conducting-circuit, a test-battery in each of such conducting circuits, each plug being adapted to be inserted into each switch in two positions or directions, in one of which said contact-piece of the plug is in connection with one of the contact-pieces of the switch and in the other of which said contact-piece of the plug is in connection with the other contactpiece of the switch, and a test receiving instrunient grounded on one side and connected on its other side to a'plug or device adapted to be brought into connection with either of said lines, substantially as set forth.

5. In a telephone-exchange system, telephone-lines grounded at their outer ends and divided into pairs retardation-coils for said lines, one retardation-coil for each line and switches for said lines, one switch for each pair of lines, each switch having two eontact-picces to which the two lines of its pair are respectively connected, and each line grounded through its retardation-coil,in combination with pairs of switch-plugs, the plugs having each a contact-piece, the two contactpieces of a pair being connected by a flexible conducting-circuit, each plug being adapted to be inserted into each switch in two positions or directions, in one of which said contact-piece of the plug is in connection with one of the contact-pieces of the switch and in the other of which said contact-piece of the plug is in connection with the other contactpiece of the switch, a test-battery in each of such flexible conducting-eircuits, and a test receiving instrument grounded on one side and connected on its other side to a plug or device adapted to be brought into connection with either of said lines, substantially as set forth.

6. In a telephone-exchange system, multiple switchboards, telephone-lines grounded at their outer ends and divided into pairs, annunciators for said lines, one annunciator for each line and switches for said lines, one switch for each pair of lines on each of said boards, each switch having two contact pieces to which the two lines of its pair are respectively connected, and each line being also grounded through its annunciator, in combination with pairs of switch-plugs at each board, the plugs having each a contact-piece, the two contactpieces of a pair being connected by a flexible conducting-circuit each plug being adapted to be inserted into each switch in two positions or directions, in one of which said contact-piece of the plug is in connection with one of the contact-pieces of the switch and in the other of which said contact-piece of the plug is in connection with the other contact-piece of the switch, a test-battery in each of said flexible conducting-circuits, and test receiving instruments,oue at each board, each grounded on one side and connected on its other side to a plug or device adapted to be brought into connection with any of said contact-pieces of said switches at its board, substantially as set forth. 7. In a telephone-exchange system, multiple switchboards, telephone-lines grounded I connected, and each line being also grounded through its annunciator and retardation-coil,

in combination with pairs of switch-plugs at 7 each board, the plugs having each a contactpiece, the two contact-pieces of a pair being connected by a flexible conducting-circuit,

each plug being adapted to be inserted into each switch in two positions or directions, in one of which said contact-piece of the plug is in connection with one of the contact-pieces of the switch and in the other of which said contact-piece of the plug is in connectionwith the other contact-piece of the switch, a testbattery in each of said flexible conducting circuits, and test receiving instruments one ateach board, each grounded on one side. and connected on its other side to a plug or device adapted to be brought into connection with any of said contact-pieces of said switches at its board, substantially as set forth. 8. In a telephone-exchange system, multiple switchboards, telephone-lines grounded at their outer ends and divided into pairs, retardation-coils for said lines, one retardationcoil for each line, and switches for said lines, one switch for each pair of lines on each board, each switch having two contact-pieces to which the'two lines of its pair are respectively con' nected, and each line being also grounded through its retardation-coil, in combination with pairs of switch-plugs at each board, the plugs having each acontact-piece, the two contact-pieces of a pair being connected by a flexible conducting-circuit each plug being adapted to be inserted into each switch in two directions or positions, in one of which said contact-piece of the plug is in connection with one of the contact-pieces of the switch andin the other of which said contact-piece of the plug is in connection with the other contactpiece of the switch, a test-battery in each of said flexible conducting-circuits, and test receivlng instruments, one at each board, each grounded on one side and connected on its. other side to a plug on device adapted to be ciators for said lines, one annunciator for each.

line, and switches for said lines one switch for each pair of lines on each board, each switch having two contact-pieces to which the two lines of its pair are respectively connected,each line being also grounded through its annunciator, in combination with pairs of switch-,- plugs at each board, the plugs having each a contact-piece and said contact-pieces of a pair being connected together by aflexible conducting-circuit, each plug having also a second contact-piece and a switching device located at its board with a contact-piece connected by a flexible conductor with said second contact-piece of the plug, each plug being adapted to be inserted into each switch in two positions or directions, in one of which its said first-mentioned contact-piece is connected with one of the contact-pieces of theswitch,and its said second -mentioned contact-piece is connected with the other contact-piece of the switch and in the other position of which said first-mentioned contact-piece of the plug is in connection with said second-mentioned contact-piece of the switch and said second-mentioned contactpiece of the plug is in connection with Said first-mentioned contact-piece of the switch, each plug being also adapted to be inserted into each of said switching devices at its board, and wheninserted to connect its said first-mentioned contact-piece with said contact-piece ot' the switching device, substantially as set. forth.

10. In a-telephone-exchange system, multi' ple switchboards, telephone-lines grounded at their outer ends and divided into pair's,- retar- -dation-coils for said lines, one retardation-coil for each line, and switches for said lines, one

1 switch for each pair of lines on each of said boards, each switch having two contact-pieces to which the two lines of its pair are respectively connected, each line being also grounded through its"retardationcoil in combination with pairs of switch-plugs at each board, the plugs having each a contact-piece and said contact-pieces of a pair being connected together by a flexible conducting-circuit, each plug having also a secondcontact-piece anda switching device located at its board with a contact-piece connected by a flexible conductor with said second contact-piece of the plug, each plug being adapted to be inserted into each switchin two positions or directions, inone of which its said first-mentioned contactpiece is connected with one of the contactpieces of the switch and its said second-mentioned contactpiece is connected with the other contact-piece of the switch and in the other position of which said first-mentioned contact-piece of the plug is connected with said second-mentioned contact-piece of the switch and said second-mentioned contact. piece of the plug is connected with said firstmentioned contact-piece of the. switch, each plug being also adapted to be inserted into each of said switching devices at its board and when inserted to connect its said first-mew tioned contact-piece with said contact-piece of the switching device, substantially as set forth.

11. In a telephone-exchange system, multiple switchboards, telephone-lines grounded at their outer ends and divided into pairs, annunciators for said lines, one annunciator for each line, and switches for said lines one switch for each pair of lines on each of said boards, each switch having two contact-pieces to which the two lines of its pair are respectively connected, and each line being also grounded through its annunciator, in combination with pairs of switch-plugs at each board, the plugs having each a contact-piece and said contactpieces of a pair being connected together by afiexible conducting-circuit, each plug having also a second contact-piece and a switching device located at its board with acontaet-piece connected through a flexible conductor with said second contact-piece of the plug, each plug being adapted to be inserted into said switches in two positions or directions, in one of which its said first-mentioned contact-piece is connected with one of the contact-pieces of the switch, and its second-mentioned contactpiece is connected with the other contact-piece of the switch and in the other position of which the said first-mentioned contact-piece of the plug is connected with the second-mentioned contact-piece of the switch and the second-nnentioned contact-piece of the plug is connected with the first-mentioned contactpiece of the switch, each plug being also ad apted to be inserted into each of said switching devices at its board and when inserted to connect its contact-piece with said contact-piece of the switching device, a test-battery in each of said flexible conducting-circuits, and test receiving instruments, one at each board, each grounded on one side and connected on its other side to a plug or device adapted to be I brought into connection with any of said contact-pieces of said switches and switching devices at its board, substantially as set forth.

12. In a telephone-exchange system, multiple switchboards, telephone-lines grounded at their outer ends and divided into pairs, retardation-coils for said lines, one for each line, and switches for said lines, one switch for each pair of lines on each of said boards, each switch having two contact-pieces to which the two lines of its pair are respectively connected, and each line being also grounded, through its retardation-coil, in combination with pairs of switch-plugs at each board, the plugs having each a contact-piece and said contact-pieces of a pair being connected together by a flexible conducting-circuit, a test-battery in each of said flexible conducting-circuits, each plug having also a second contact-piece and a switching device located at its board with a contactpiece connected through a flexible conductor with said second contact-piece of the plug,

each plug being adapted to be inserted into each switch at its board in two positions or directions, in one of which its said first-mentioned contact-piece is connected with one of the contact-pieces of the switch and its said second-mentioned contact-piece is connected with the other contact-piece of the switch and in the other of which its said first-mentioned contact-piece is connected with the second-mentioned contact-piece of the switch and its said second-mentioned contact-piece is connected with the first-n1entioned contact-piece of the switch, each plug being also adapted to be inserted into each of said switching devices at its board and when inserted to connect said first-mentioned contact-piece oi the plug with said contact-piece of the switching device, and test receiving instruments, one at each board, each grounded on one side and connected on its other side to a plug or device adapted to be brought into connection with any of said contact-pieces of said switches and switching devices at its board, substantially as set forth.

13. In a telephone-exchange system, multiple switchboards, telephone-lines divided into pairs, annunciators for said lines, one annuneiator for each line, and switches for said lines, one switch on each board for each pair of lines, each switch having two contact-pieces to which the two lines of its pair are respectively connected and each line being grounded through its annunciator, in combination with two switch-plugs at any board, the contact-pieces of which are connected together by flexible conductors. said plugs being inserted into two of said switches to connect together two of said lines for conversation between the subscribers into a circuit which does not include their annunciators, and a clearing-out annunciatorin circuit with either or both lines thereby connected together, substantially as set forth.

14:. In a telephone-exchange system, multiple switchboards, telephone-lines divided into pairs, retardation-coils for said lines, one retardation-coil for each line and switches for said lines, one switch on each board for each pair of lines, each switch having two contactpieces to which the two lines of its pair are respectively connected and each line being grounded through its retamlation-eoil, in eon1- bination with two switch-plugs at any board, the contact-pieces of which are connected together by flexible conductors, said plugs being inserted into two of said switches to connect together two of said lines for conversation l etween the subscribers into a circuit which does not include their retardation-coils, and a clearing-out annunciator in circuit with either or both lines thereby connected together, substantially as set forth.

15. In a telephone-exchange system, 1nultiple switchboards, telephone-lines divided into pairs, annunciators and retardation-coils for said linesone annunciator and one retardation-coil for each line and switches for said lines, one switch for each pair of lines, each switch having two contact-pieces to which the two lines of its pair are respectively connected, and each line being grounded through its annunciator and retardation-coil, in combinat'ion with two switch-plugs at any board, the contact-pieces of which are connected together by flexible conductors, said plugs being inserted into two of said switches to connect together two of said lines for conversation between the subscribers into a circuit which does not include their annunciators and retardation-coils, and a clearing-out annunciator in circuit with either or both lines thereby connected together, substantially as set forth.

16. In a telephone-exchange system, the combination of telephone lines, a generator and apparatus at each subscribers station to at will generate two kinds of currents, a calling-current and a clearing-out current, their I switching devices on aboard of the exchange, annunciators for the lines each in a connection from its line to ground and adapted to respond to calling-currents, but not to clearing-out currents, means for connecting two lines together for a conversation, a clearingout annunciator, means for connecting 1t 1n the direct circuit of two connected lines, sa d annunciator being adapted to respond to clearline connected at the central office in a connection from its line to ground, devices at each subscribers statlon for sendlng currents over the line of one polarity to operate the line-annunciator, means for connecting two lines together for conversation, a clearing-out annunciator at the central oflice, circuit connections whereby it is included in the direct circuit of two connected lines, and means whereby either subscriber may send over theline a. current of the other polarity that will not operate the calling-annunciators, but will operate the clearing-annunciator, substantially as set forth. I

-19. In a telephone-exchange system, the combination of two telephone-lines connected together for conversation, their calling-an-' nunciators through which they are then, or as long as thus connected, grounded, and a clearcircuit of said lines, the calling-annunciators being adapted not to respond to clearing-out currents, substantially as set forth.

20. In a telephone-exchange system, telephone-lines divided into pairs, ann'unciators for said lines, one annunciator for each line,

,ing-out annunciator connected in the direct and switches for said lines, one switch for each pair of lines, each switch having two contact pieces to which the two lines of its pair are respectively connected, and each line being grounded through its annunciator, in combination with pairs of switch-plugs, the plugs having each a contact-piece and the two contactpleces of each pair being connected together by aflexible conducting-circuit, each plug being adapted to be inserted into each switch in two positions or directions, in one of which its said contact-piece is connected with one of the contact-pieces of the switch and in the other of which the contact-piece of the plug is connected with the other contact-piece of the switch, substantially as set forth. 21. In a telephone-exchange system, telephone-lines divided into pairs,annu nciators and retardation-coils for said hnes, one annunciator and one retardation-coil for each l ne, and switches for said lines on a sw1tch-' board, one switch forleach pair of lines, each switeh',having two contact-pieces to which the two lines of its pair are respectively connected, and each line being grounded through its annunciator and retardation-coil, in combination with pairs ofswitch-plugs, the'plugs having each a contact-piece and the two contact-pieces of each pair being connected together by a flexible conducting-circuit, each plug being adapted to be inserted into. each switch in two positions or directions, in one of which its said contact-piece is connected with one of the contact-pieces of the switch and in the othero-f which the contact-piece of the plug is connected with the other contact piece of the switch, substantially as set forth.

22. In a telephone-exchange .system, telephone-lines divided into pairs, 'annunciators for said lines, one annunciator for eachline, andv switches .for said lines ,on a switchboard, one switch for eachpair oflines, eachswitch havingtwo contact-pieces to which the two lines of its pair are respectively connected each line being grounded through 1ts annun' ciator, in combination with pairs of switchplugs having each a contact-piece and said contact-pieces of a pair being connected by a flexible conducting-circuit, each plug having also a second contact-piece and a switching device with a contact-piece to which said second contact-piece of the plug is connected by a flexible conducting-circuit, each plug being adapted to be inserted into each switch in two positions or directions, in one of whichits first-mentioned contact-piece" is connected to" one of the contact-pieces ofthe switch and its second-mentioned contact-piece" is connected with the other contact-piece of the switch, and in the other of which the first-mentioned contact-piece of the plug is connected with the second-mentioned contact-piece of the switch and the second-mentioned contact-piece of the plug is connected with the first-mentioned contact-piece of the switch, each plug being also adapted to be inserted into each of said switching devices and when inserted to connect its first-mentioned contact-piece with ing each a contactpiece and said contactpieces of a pair being connected by a flexible conducting-circuit, each plug having also a second contact-piece and a switching device with a contact-piece connected with said second contact-piece of the plug through a flexible conducting-circuit, each plug being adapted to be inserted in two positions or directions in each switch, in one of which positions said first-mentioned contact of the plug is connected to one of the contact-pieces of the switch and said second-mentioned contact-piece of the plug is connected with the other contactpiece of the switch, and in the other of which said first-mentioned contact-piece of the plug is connected with said second-mentioned contact-piece of the switch and said second-mentioned contact-piece of the plug is connected with said first-mentioned contact-piece of the switch, each plug being also adapted to be iriserted into each of said switching devices, and when inserted, to connect its first-mentioned contact-piece with said contact-piece of the switching device, substantially as set forth.

24:. In a telephone-exchange system, telephone-lines divided into pairs, annunciators for said lines, one annunciator for each line, and switches for said lines, one switch for each pair of lines, each switch having two contactpieces to which the two lines of its pair are respectively connected and each line being grounded through its annunciator, in combination with two switch-plugs, the two contactpieces of which are connected together by flexible conductors, said plugs being inserted into two of said switches to connect two of said lines for conversation between the subscribers into a circuit which does not include their annuneiators, substantially as set forth.

25. In a telephone-exchange system, telephone-lines, divided into pairs, retardationcoils for said lines, one retardation-coil for each line, and switches for said lines one switch for each pair of lines, each switch having two contact-pieces to which the two lines of its pair are respectively connected, and each line being grounded through its retardation-coil, in combination with two switch-plugs, the two contact-pieces of which are connected together by flexible conductors, said plugs being inserted into two of said switches to connect two of said lines for conversation between the subscribers into a circuit which does not include their retardation-coils.

26. In a telcphone-exchange system, telephone-lines divided into pairs, annunciators and retardation-coils for said lines, one annunciator and one retardation-coil for each line, and switches for said lines, one switch for each pair of lines, each switch having two contact-pieces to which the two lines of its pair are respectively connected and each line being grounded through its annunciator and retardation-coil, in combination with two switch-plugs, the two contact-pieces of which are connected together by flexible conductors, said plugs being inserted into two of said switches to connect two of said lines for conversation between the subscribers into a circuit which does not include their an nunciators and retardation-coils.

In testimony whereof .I have hereunto subscribed my name.

Ml LO (1i. KELLCX l l.

Witnesses:

FRANK S. Oman, EDWARD C. DAVIDSON. 

